The finer points are minor, such as the MKII (empeg) knob is more clickey and more likely to fail while the MKIIa (RioCar) knob is smoother and more robust (yes yes, "knob" = "rotary encoder"). Also, the MKII (empeg) sled (and body?) metal is apparently better than the MKIIa (RioCar), letting the empeg enter and leave the sled with less grinding, "fingernails on the chalkboard" feeling. The empeg's 12 meg RAM vs. the RioCar's 16 meg is listed in the FAQ, but can be overcome using a 64meg memory card (link?).